1. Field of the Invention
The invention relates to an improved method and apparatus for detecting fecal contamination on the surface of produce using visible light fluorescent spectroscopy.
2. Description of the Prior Art
Microbial pathogens in food cause an estimated 6.5 million to 33 million cases of human illness and up to 9,000 deaths annually, according to the Council for Agricultural Science and Technology. Furthermore, the USDA Economic Research Service has recently reported that the annual cost of the food borne illnesses caused by six common bacterial pathogens, Campylobacter spp., Clostridium perfringens, Escherichia coli 0157:H7, Listeria monocytogenes, Salmonella spp., and Staphylococcus aureus, ranges from 2.9 billion to 6.7 billion dollars (Food Institute Report, USDA, AER, December, 1996).
Feces are the primary source of pathogenic E. coli contamination of agricultural commodities, and both FDA1 and FSIS2 use the presence of E. coli as an indicator of fecal contamination. The adverse health risks of pathogenic organisms originating from feces, including E. coli O157:H7, in foods are well documented.3-7 
Although the foods most typically associated with these illnesses are animal products such as red meat, poultry and eggs, seafood, and dairy products, fruits and vegetables, and particularly apples used to make juice, have faced increased scrutiny as potential sources of illness for consumers. For example, fruits and vegetables are commonly contaminated with fecal material during the spreading of manure.
Fluorescence sensing techniques are widely used in a number of scientific applications including cell biology, photochemistry, medicine, and environmental sciences.8-11 Plant materials including leaves and fruits exhibit fluorescence emissions in the visible (VIS) region of the spectrum when excited with appropriate radiation.12-15 Fluorescence emission peaks (maxima) from these materials are typically observed in the blue, green, red, and far-red regions of the spectrum at approximately 450, 530, 685, and 735 nm, respectively. We have demonstrated that feces show similar responses, and that responses from feces from different species of agricultural interest are similar.16 
In prior studies, we have demonstrated that fecal contamination of apples can be detected based on differential fluorescence responses of feces and normal apple surfaces.13,17 We have developed a multispectral laser-induced fluorescence imaging system, which has been used to detect fecal contamination of apples.17,18 The system used a UV pulsed laser to excite samples and an intensified camera to record fluorescence responses. A specific advantage of this pulsed-laser system is that images from samples with low quantum yields can be acquired very rapidly regardless of ambient light conditions.
However, despite these advances, there remains a continuing need for a high-speed system capable of detecting feces on fruits and vegetables in real-time during processing.